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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Rapid and Temporary Deployment of Fiber-Optic Arrays to Measure Surface Chemical Explosion Series with Distributed Acoustic Sensing

Rapid and temporary distributed acoustic sensing (DAS) deployments are crucial for accurately capturing the seismic wavefield following major events, such as earthquakes, or in anticipation of known events of interest, such as chemical explosions. We provide an overview of two DAS campaigns conducted in May and October 2024 to record the seismoacoustic waves generated by two series of surface chemical explosions in New Mexico, United States, involving 1- and 10-ton trinitrotoluene-equivalent charges. In both campaigns, we deployed approximately 2 km of fiber-optic cables in a dry riverbed, about 12 km east of the explosion sites. For the October campaign, seven geophones and two anemometers were collocated with the fiber. We describe the field deployments and present preliminary results from the recorded signals. Specifically, we cross analyze the data recorded in May and October, validate the DAS data with geophone measurements, and highlight the benefits of burying fibers to reduce wind noise and improve signal-to-noise ratios. This study demonstrates the potential of DAS to record the seismoacoustic waves generated by surface chemical explosions of varying sizes at distances of approximately 10 km from the source.

58 GEOSCIENCES↗
NASA NTRS1994

Propagation of whistler waves driven by fine structured ion beams in the magnetotail

In a previous paper, which examined the propagation of low-frequency whistler waves generated by ion beams in the Earth's plasma sheet boundary layer (PSBL), it was found that whistler waves driven in the PSBL are focused toward the central plasma sheet due to the global magnetotail inhomogeneities; this finding may help explain the observations of magnetic noise bursts in the tail (Burinskaya et al., 1993). In this paper the same phenomenon is examined, but this time a much more realistic model is used for the ion beam in the PSBL. While the PSBL has been modeled as a solid, homogeneous ion beams with a width of one Earth radius, observations and theoretical considerations have shown that PSBL ion beams actually have a decreasing velocity profile toward the plasma sheet and that the density of the beams within the PSBL can vary locally. We consider again the propagation and generation of electromagnetic waves but in the presence of fine structured ion beams in the PSBL. Our results show that whistler waves, generated quasi-parallel to the background magnetic field, can be trapped locally within small spatial regions where the ion beam density is enhanced compared to the density of the adjacent PSBL region. Wave spectra and nonlinear saturation mechanisms are discussed.

Burinskaya, T.↗
DOE OSTI2024

Theory, analysis, and testing of an angular resonator for wave energy generation

This article describes the theory, analysis, and initial bench-top testing of a minimally invasive, rotational resonator designed to produce small amounts of electrical energy for use in oceanic observation buoys. Here, this work details the systems of equations that govern such a resonator, its potential power production, and its predicted effects on the modified motion of the buoy. Finally, a bench-top test apparatus is designed and experimented upon to identify the system and verify the system of equations empirically.

16 TIDAL AND WAVE POWER↗
DOE OSTI2020

Generation of waves in magnetized plasma [PowerPoint]

The presentation goes through assumptions made for the study, sections on plasma dispersion, whistler modes for RBR, excitation of plane waves with antenna, dipole vs loop antenna, verification of results, excitation of whistler waves with electron beams, assumptions for the model, distribution of current in space in general case, Fourier transform of current distribution, resonant excitation of waves, and ending with a discussion of generic debunching.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1969

Wide-band doubler and sine wave quadrature generator

Phase-locked loop with photoresistive control, which provides both sine and cosine outputs for subcarrier demodulation, serves as a telemetry demodulator signal conditioner with a second harmonic signal for synchronization with the locally generated code.

Crow, R. B.↗
NASA NTRS1969

Dispersion of ion-acoustic waves

Dispersion of ion-acoustic waves in quiescent rare gas discharge plasmas, discussing model simulating ion waves generated by finite sine wave bursts

Alexeff, I.↗
NASA NTRS1974

A technique for generating shear waves in cylindrical shells under radial impact

Experimental techniques are developed to study and measure the shear-wave velocity in an aluminum cylindrical shell subjected to a radial impact. The radial impact is obtained by exploding an electrical detonator inserted in plastic plugs mounted on the end of the shell. Strain gages, mounted on the outside surface of the shell at various axial locations, are used to obtain oscilloscope traces from which the shear-wave velocity can be calculated.

Blum, A.↗
NASA NTRS1981

Measurements of a solar flare-generated shock wave at 13.1 R/0/

The first measurements of the structure of wind speed, electron density, and electron density fluctuations are reported for a shock wave propagating through the acceleration region of the solar wind. Radio scattering observations, consisting of spectral broadening, mean phase and amplitude scintillations, were made on August 18, 1979, 13.1 solar radii east of the sun near the ecliptic plane, using the 2.3 and 8.4 GHz radio signals of Voyager 1. The results show a shock wave speed of about 3,500 km/sec; which, when compared with average transit time speed to 1 AU, shows that substantial deceleration took place with outward propagation from the sun. This result is consistent with a blast wave.

Woo, R.↗
NASA NTRS1981

Interpretation of phase velocity measurements of wind-generated surface waves

Differences in experimental results for surface gravity wave phase speeds obtained by cross spectra and slope-height spectra are compared. It is shown that, for a simple two-dimensional model containing both dispersive and non-dispersive waves, the observed differences can be explained readily. The slope-height technique measures a weighted average of the wavenumber squared; for frequencies sufficiently large compared with the dominant frequency, the computed phase-speed variation with frequency is representative of the wave having the larger wavenumber - the dispersive wave. For the cross-spectral method, it is shown that the small-probe-separation assumption usually employed is not valid for frequencies much larger than the dominant frequency, except at the singular point where both waves have exactly equal spectral densities and the phase function represents an average of the two modes. For all other cases, the phase function approaches that of the wave having the larger spectral density, and essentially ignores the presence of the other wave, even if both modes are relatively close in their contributions to the total spectral density.

Dudis, J. J.↗
NASA NTRS1988

Microwave and millimeter-wave power generation in silicon carbide avalanche devices

Numerical simulations were performed to investigate the typical power-generating capabilities of SiC IMPATT diodes. Using available material parameters, SiC double-drift IMPATT diodes were simulated at 10, 35, 60, and 94 GHz, and the operating characteristics of these devices were compared to those of Si and GaAs devices. Compared to the Si and GaAs IMPATT performances in the pulsed mode, the SiC IMPATT performance was found to be far superior. The performance of SiC devices in the CW mode was also superior to that of GaAs devices, especially at lower frequencies. At a high frequency (94 GHz), the performance of the SiC device was found to be comparable to that of Si devices.

Mehdi, I.↗
NASA NTRS1989

Microwave and millimeter-wave power generation in silicon carbide (SiC) IMPATT devices

There are two points that should be noted. First, in the thermal resistance calculations it is assumed that the device is operating at 773 K while the results of the room temperature simulations are used. This was done because there is not enough information to correctly predict the material parameters at 773 K. Since, in general, device performance degrades with increasing temperature, the cw results are perhaps a bit optimistic. Second, the electric field in these structures gets extremely high and there might be some possibility of tunneling. This was not incorporated into the simulation. Again, this could result in different device operating conditions.

Mehdi, I.↗
NASA NTRS1989

Report from space plasma science

Space plasma science, especially plasma experiments in space, is discussed. Computational simulations, wave generation and propagation, wave-particle interactions, charged particle acceleration, particle-particle interactions, radiation transport in dense plasmas, macroscopic plasma flow, plasma-magnetic field interactions, plasma-surface interactions, prospects for near-term plasma science experiments in space and three-dimensional plasma experiments are among the topics discussed.

Hastings, D. E.↗